1. Field of the Invention
This invention relates to a data communication method, specifically to a date communication method suitable for use in a camera.
2. Description of Related Art
Due to recent advancement of automatization for cameras, cameras provided with an auto-focus (AF) system and an auto-exposure (AE) system have increasingly been produced. Nowadays, however, higher function is demanded for a camera. For example, shortening focalizing time, increasing accuracy of focalizing, a complex, various kinds of programmed exposure modes, such as shutter speed priority mode for telephoto lens, object depth priority mode for wide angle lens, etc., and display apparatus of a larger size enabling a user to recognize at a glance a various photograph information, such as number of frames of film to be photographed, programme mode, etc. are demanded. Further and in order to increase accuracy of focalizing for AF (Auto-focus) device, increase in the number of CCD (Charge Coupled Device), increase in lens information, and higher calculation processing are required. Under these circumstances, difficulties have been experienced in performing various functions of memorizing data, calculation or processing of data and controlling a system by means of a single microcomputer.
In order to eliminate the above problems, it will be possible to provide plural microcomputers so as to share the above functions with them. For example, it is possible to provide a main microcomputer, together with one or more of sub-microcomputers, thus entrusting the main microcomputer with a system control function for generally controlling sequential operation of a camera and a distance measurement and calculation function, while entrusting the one or more of sub-microcomputers with a photometric calculation function, a data input control, a data-memorizing function, a display control function, etc., whereby sharing functions of calculation, control and memorizing with the plural microcomputers so as to increase processing efficiency.
The above system however requires a numerous number of data transmission between the main microcomputer and the sub-microcomputers and hence it is necessary to allot a several numbers of communication lines for data communication to each of the main microcomputer and sub-microcomputers. Furthermore and in order to achieve accurate data transmission, it is necessary to employ control line such as a communication request line, busy line, etc., or it is also necessary to employ a synchronous clock or a system clock for an asynchronous communication with a greatly higher accuracy. Furthermore, a signal for control line communication other than serial transmission lines is required in order to perform serial data communication between the main microcomputer and sub-microcomputers, thus requiring at least three communication lines for performing data communication. Accordingly, inconveniency in which, for example, ports for information processing are uselessly utilized, might occur.
When it is intended to photographing with plural light sources, it is necessary to connect the camera and flash with a cable for exclusive use of plural light sources. This results in time-consuming setting and inconveniency. There is another type of system, particularly intended for photographing wild birds, in which such a connection cable is obviated and infrared light is output from an external accessary for remote control, thus enabling a camera to release. In such a type of system, however, only an operation of release is permitted, and thus it is not possible to set up photograph mode and/or exposure rectification from a position remote from the camera body, nor to permit monitoring of number of photographable frames of film and/or brightness of an object.